Garth Carroll, who calls himself Professor Gizmo, wears the American flag as he demonstrates at Occupy Seattle at Westlake Park in downtown Seattle, Washington. Photograph: Marcus Donner/REUTERS

The Wall Street protests against economic inequality and corporate greed that targeted the nerve centre of American capitalism are no longer merely a New York phenomenon. This weekend, from Seattle and Los Angeles on the west coast to Providence, Rhode Island, and Tampa, Florida, on the east, as many as 70 major cities and more than 600 communities have joined the swelling wave of civil dissent. The slogan "Occupy Wall Street" has been suitably abbreviated to a single word: "Occupy"

"This could be the tipping point," said Dick Steinkamp, 63, a retired Silicon Valley executive at the Occupy Seattle protest being held in the heart of the city's shopping and restaurant district . He and his wife had driven two hours from their home in Bellingham, north of Seattle, specifically to join the rally and give it support from more conventional professionals.

"I marched against the Vietnam war before I was drafted into the army and this movement is now getting towards that critical mass," he said.

One of the favourite messages of the protesters is that almost 40% of US wealth is held in the hands of 1% of the population, who are taxed more lightly than the majority of Americans. Steinkamp was holding a sign saying "I am the 99%". And there is widespread anger that ordinary people have born the brunt of the financial crisis with dire job losses and house repossessions.

"I came here because I wanted to show it wasn't just young anarchists," said Deb Steinkamp, also 63 and a retired marriage counsellor, wearing a green cagoule and sensible shoes against the damp, chilly Seattle weather.

Protests broke out last week in Chicago, Boston, Memphis, New Orleans, Las Vegas, Philadelphia, Austin, Louisville, Atlanta and dozens of other cities. Vancouver, Toronto, Montreal and Calgary are set to add themselves to the ranks next weekend.

Motorists honked their support as they passed the Seattle demonstration, which was around 500 strong on Friday and likely to swell as the weekend progressed. Earlier in the week the police forced protestors to clear away tents that had been multiplying across the square. Seattle's liberal mayor Mike McGinn supports the protesters – but drew the line once they started camping in the middle of downtown.

In New York more than 700 people have been arrested while marching on the stock exchange and over the Brooklyn Bridge in the name of Occupy Wall Street and 20,000 marched in lower Manhattan last Wednesday.

The sheer proliferation of the rallies across 45 states has drawn attention. "It expresses the frustrations the American people feel about the biggest financial crisis since the Great Depression," President Obama said. "There has been huge collateral damage all across 'Main Street' [from the financial crisis] and some of the same folks who acted irresponsibly are now trying to fight a crackdown on the abusive practices that got us into this in the first place," he added.

In Los Angeles mayor Antonio Villaraigosa handed out rain ponchos to demonstrators when there was a downpour. A thousand people gathered outside the city government offices for Occupy Austin, as well as similar crowds in Dallas and Houston.

After joining Occupy Wall Street, alongside a group of university professors, Obama's former head of blog campaigns Sam Graham-Felsen pointed out that the movement was maturing. He said that although it would not have started without radical idealists taking to the streets it has gone to the next level with the inclusion of "seasoned organisers and pragmatists".

Asher McCord, 31, a shopworker in Seattle, was at the protests before starting his shift at a department store, and was wearing a neat woollen blazer and designer jeans. "There is that saying, 'Dissent is patriotic,' and I agree with that. I was unemployed for a while. I just started my new job and I think lower income people are taking all the pain and the anxiety in this recession," he said.

Protesters are complaining about tax breaks for oil companies, excessive lobbying in Washington, astronomical pay and bonuses for financiers, and the bailout of the banking sector.

The movement was sparked in part by Vancouver-based Adbusters Media Foundation, an anti-consumerism organ with a magazine, which urged people to occupy Wall Street to protest inherent inequalities in the economic system. There is no central organisation or formal co-ordination between cities but instigators use web tools such as Twitter and Facebook to pass information and now hope that the demonstrations will build towards the G20 economic summit in Cannes next month.

Detractors have mocked protesters for using social media, when those brands are increasingly corporatised. But hospital nurse Angela Silling, 41, who was staffing the first aid post in Seattle's Westlake Park, said: "The Arab Spring demonstrators used social media very successfully and no one has criticised those rebels."

House of Representative majority leader Eric Cantor dismissed the protesters as "mobs" who were prompting "Americans to fight Americans". That prompted a storm of criticism, because he has praised the Tea Party as a legitimate expression of conservative grassroots anger.

Seattle demonstrator Ted Lang, 26, who has just qualified as an English teacher and is considering moving abroad, said the Occupy demonstrators had much in common with the libertarians who first started the Tea Party movement. "But it got hijacked by right-wing religious conservatives," he said.